Flywheels are generally known in the art for storing energy. While flywheel energy storage devices have been used for many years in satellite or other spacecraft applications, more recently they have been adapted for use on terrestrial machines. More specifically, hybrid power plants have been proposed which use a combustion engine as the primary mover and a flywheel as a secondary mover.
While early flywheels were formed of a metal material, more recently flywheels have been proposed that are formed of different materials that may increase the energy storage capacity of the flywheel. For example, flywheels may be formed of a carbon fiber material that has a higher strength-to-weight ratio and therefore can rotate at higher speeds (such as, for example, approximately 60,000 rpm or more). The higher rotational speeds increase the storage capacity of the flywheel.
The rotational speed of the flywheel is relatively high when compared to the output of a typical engine for a machine. For example, flywheel speeds are generally in the range of 10,000-60,000 rpm, while engines will typically operate at speeds of approximately 500-2,000 rpm. To accommodate for this difference in speeds, conventional flywheel systems will often incorporate a continuously variable transmission (CVT) or other similarly elaborate assembly to interface between the flywheel and the other powertrain components. For example, while U.S. Pat. No. 4,680,986 to Elsner discloses a flywheel coupled to an engine, a series of mechanical devices, including a hydrodynamic coupling, are disposed between the engine and the flywheel. Consequently, the efficiency of energy transfer between the flywheel and the engine is decreased.